| In this paper, polycarboxylate superplasticizers were modified by the hyperbranched poly(amid-amine) (PAMAM) with highly branched chain structure. PAMAM was grafted to both sides of comb-type polycarboxylate superplasticizers molecular chain. Polycarboxylate superplasticizers with carboxyl groups in both sides of the main chains were obtained with 4, 4'-Azobis (4-cyanovaleric acid) (ACVA) as the initiator, sodium methylallyl sulfonate (MAS), allyloxy polyethylene glycol (APEG) and tertiary butyl methacrylate (TMBA) as the monomers in the N, N-Dimethylformamide (DMF) solution. Then hyperbranched-type polycarboxylate superplasticizers (HPC) were prepared by grafting polymerization with ethylenediamine (EDA) and acrylic acid (AA) as monomers in both sides of polycarboxylate superplasticizers molecular chain. The generation of PAMAM was controlled via adding alternately monomers several times during the process of polymerization. HPC had spherical hyperbranched structure in both sides of the chains. This structure of molecular contained more active groups (carboxyl and amino). Thus it had larger contacted area with the surface of cement particles that made the combination between superplasticizers molecules and cement particles more solid. Hyperbranched spherical structures could increase the steric effect, which enhanced the dispersion stability of cement particles and improved disadvantages of instability and poor adaptability in the application of polycarboxylate superplasticizers widely.The hyperbranched-type polycarboxylate superplasticizers were characterized by IR spectra and 1HNMR spectra. IR and 1HNMR spectra indicated that HPC was synthesized successfully. Experimental conditions on reaction temperature, reaction time, initiator dosage, monomer ratio, molecular weight of APEG and hyperbranched generation were discussed. Hyperbranched-type polycarboxylate superplasticizers were applied into the cement concrete. Fluidity of cement paste was tested. The experimental data showed that: the synthetic hyperbranched-type polycarboxylate superplasticizers had the highest fluidity of cement paste under these conditions: the monomer ratio of MAS: TBMA: APEG = 1 : 5 : 0.5, the initiator amount of 5.0%, PAMAM G 4.5, APEG of 700 molecular weight, reaction temperature of 80℃, reaction time of 5 h. These showed that the above condition was the best reaction condition.A series of synthetic hyperbranched-type polycarboxylate superplasticizers were applied into the cement concrete. Performance of HPC such as surface tension, saturated content of superplasticizers, water-reducing rate, loss of fluidity by the time, slump, adaptability in different cements, compressive strength of cement concrete and setting time of concrete were tested. The results showed that: the hyperbranched-type polycarboxylate superplasticizers could largely reduce the surface tension of water. Cement paste had high fluidity, water-reducing rate and the slump in the case of low HPC content. And the superplasticizers had good fluidity retention by the time. Setting time after mixing of hyperbranched-type polycarboxylate superplasticizers significantly was extended, which indicated that the superplasticizers had good retarding effect. After 3d, 7d, 28d compressive strength tests, cement concrete with HPC had high compressive strength ratio compared with the basic concrete. Four kinds of different cement concretes with HPC had good performance after being tested, which showed that hyperbranched-type polycarboxylate superplasticizers had good adaptability. Performances of synthetic hyperbranched-type polycarboxylate superplasticizers and polycarboxylate superplasticizers on the market were compared. The result showed that: hyperbranched-type polycarboxylate superplasticizers improved greatly the performance on water-reducing rate, fluidity of cement paste and compressive strength ratio compared with our country's products. Compared with foreign products, water-reducing rate and fluidity of cement paste increased obviously.
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